FPS drop in Dota 2

When I play Dota 2 I experience fps drop whenever there is a team fight or 3 or more heroes present in the screen. Normally Dota runs at about 80 fps but during team fights it drops to mere 20. My laptop specs are as follows:

• Processor: Intel Core i7-5500U
• CPU @2.4GHz
• RAM: 8gb
• Graphics card: 2gb, AMD Radeon R5 M330

I play at minimum graphics with everything turned off, still, I face FPS drop. Any suggestions for this problem?